Video camera with aperture blade

ABSTRACT

A video camera ( 10 ) includes a photographing device ( 16 ). The photographing device ( 16 ) generates an image signal corresponding to an optical image irradiated on a light-receiving surface, and a monitor ( 34 ) displays a moving image based on a generated image signal. An amount of incident light into the photographing device ( 16 ) is controlled by an aperture apparatus ( 14 ) having an aperture blade that moves to a direction perpendicular to a light axis. A moving amount of the aperture blade is restricted by a predetermined value, and this defines a minimum value of an F number. When the moving image is displayed on the monitor ( 34 ), it is prohibited to set to the minimum value of the F number.

TECHNICAL FIELD

[0001] The present invention relates to a video camera. Morespecifically, the present invention relates to a video camera providedwith a mechanical aperture apparatus in which a size of an openingportion is changed by an aperture blade, such as a digital camera, avideo tape recorder combined with a camera.

PRIOR ART

[0002] In a mechanical aperture apparatus such as a Galvano apertureapparatus, a size of an opening portion of an aperture blade, i.e., an Fnumber is feedback-controlled based on an output signal of a sensor thatdetects a brightness of an object or a luminance component of an imagesignal outputted from a photographing device. This adjusts the F numberin such a manner that an incident light amount becomes an optimum value.

[0003] In such the aperture apparatus, the aperture blade is driven insuch a manner that a pin formed on the aperture blade is pressed againsta terminal of a long hole to which the pin is attached when setting theF number to a minimum value. However, when pressing the pin against theterminal, maximum voltage of a driving capability is outputted from adriver of the aperture apparatus, thus giving rise to a problem that aconsumed electricity becomes large.

[0004] Meanwhile, in an electronic still camera that uses an apertureapparatus as a mechanical shutter apparatus by fully closing theaperture blade in high speed by reverse energization, responsivecharacteristic of the aperture blade is quite different between a casethat the aperture blade is fully closed from a state that the pin ispressed against the terminal, and a case that the aperture blade isfully closed from a state that the pin is set to a position immediatelybefore contacting the terminal. In general, although a sensor fordetecting the F number is incorporated in a camera, it is impossible todistinguish the state that the pin is pressed against the terminal, andthe case that the pin is set to the position immediately beforecontacting the terminal because a characteristic of the sensor differs.As a result, it was not possible to exactly control an exposure timeperiod in a state that the F number is set to a vicinity of the minimumvalue.

[0005] Furthermore, in an aperture apparatus in which the aperture bladeis feedback-controlled based on the F number detected by a hole element,a transient response by a hole effect occurs to an output of the holeelement if a moving amount of the aperture blade is large. As a result,this led to a problem that the aperture amount is not exactlycontrolled.

SUMMARY OF THE INVENTION

[0006] Therefore, it is a primary object of the present invention toprovide a novel video camera.

[0007] It is another object of the present invention to provide a videocamera capable of preventing a consumed electricity from increasing inan aperture control.

[0008] It is still another object of the present invention to provide avideo camera capable of exactly controlling an exposure time period whenusing an aperture apparatus as a mechanical shutter apparatus.

[0009] It is yet still another object of the present invention toprovide a video camera capable of exactly controlling an apertureamount.

[0010] A video camera according to the present invention, comprises: animage sensor for generating an image signal corresponding to an opticalimage irradiated onto a light-receiving surface; a display means fordisplaying in real time a moving image based on the image signal; anaperture blade for adjusting an amount of an incident light into theimage sensor by moving toward a direction perpendicular to a light axis;a restricting member for restricting a moving amount of the apertureblade by a predetermined value in order to define a minimum value of anF number; and a prohibiting means for prohibiting a setting of the Fnumber to the minimum value when the moving image is displayed.

[0011] The image sensor generates an image signal in response to anoptical image irradiated onto a light-receiving surface, and the displaymeans displays a moving image based on a generated image signal. Anamount of an incident light into the image sensor is adjusted by theaperture blade that moves toward a direction perpendicular to a lightaxis. A moving amount of the aperture blade is restricted by arestricting member by a predetermined value, which defines a minimumvalue of the F number. When the moving image is displayed by the displaymeans, a setting of the F number to the minimum value is prohibited.

[0012] Preferably, the aperture blade has a hole extending to a movingdirection, and the restricting means has a protruding portion engagedwith the hole. The moving amount of the aperture blade is restricted asa result of a terminal of the hole contacting the protruding portion.

[0013] In a case that power is transmitted to the aperture blade by amotor, it is possible to restrain a consumed electricity by prohibitinga setting of the F number to the minimum value.

[0014] According to the present invention, a video camera that adjustsan exposure amount of an image sensor in response to an exposureadjusting instruction, and records a still image signal generated by theimage sensor in response to a recording instruction, which is after theexposure adjusting instruction, comprises: an aperture blade foradjusting an amount of an incident light into the image sensor by movingtoward a direction perpendicular to a light axis; a controlling meansfor controlling the aperture blade in order that an F number is out of apredetermined range when the exposure S adjusting instruction isapplied; and a cutting-off means for cutting-off an incident light intothe image sensor by fully closing the aperture blade when the recordinginstruction is applied.

[0015] An amount of the incident light into the image sensor is adjustedby the aperture blade that moves toward a direction perpendicular to thelight axis. When the exposure adjusting instruction is applied, thecontrolling means controls the aperture blade in such a manner that theF number is out of the predetermined range. When the recordinginstruction is applied after the exposure adjusting instruction, theaperture blade is fully closed by the cutting-off means. This cuts-offthe incident light into the image sensor.

[0016] In a case of defining a minimum value of the F number byrestricting the moving amount of the aperture blade by a predeterminedvalue, and cutting-off the incident light by transmitting power to theaperture blade, the predetermined range is present in the vicinity ofthe minimum value. Preferably, the aperture blade has a hole extendingtoward a moving direction, and the restricting member has a protrudingportion attached to the hole. The moving amount of the aperture blade isrestricted as a result of the terminal of the hole contacting protrudingportion.

[0017] In the vicinity of the minimum value, a required time period forthe aperture blade to fully close drastically varies. It makes itpossible to exactly control the exposure time period by controlling theaperture blade in such a manner that the F number is out of such therange.

[0018] In a case of calculating the optimum F number that defines anoptimum exposure amount when the exposure adjusting instruction isapplied, and setting the exposure time period that defines apredetermined F number and the optimum exposure amount when the optimumF number is included in the predetermined range, the controlling meanscontrols the aperture blade so as to indicate a predetermined F number.It is noted that preferably the predetermined F number is a minimum Fnumber.

[0019] A video camera according to the present invention, comprises: animage sensor for generating an image signal corresponding to an opticalimage irradiated onto a light-receiving surface; an aperture blade foradjusting an incident light amount into the image sensor by movingtoward a direction perpendicular to a light axis; a calculating meansfor calculating an optimum F number of the aperture blade based on theimage signal; and a changing means for gradually changing the F numberof the aperture blade to the optimum F number.

[0020] The image sensor generates the image signal corresponding to theoptical image irradiated onto the light-receiving surface, and anaperture member adjusts an incident light amount into the image sensorby moving toward a direction perpendicular to the light axis. If thecalculating means calculates the optimum F number of the aperture bladebased on the image signal, the F number of the aperture blade isgradually changed to the optimum F number by the changing means.

[0021] In a case that a voltage signal corresponding to the F number ofthe aperture blade is outputted from a hole element, the changing meanschanges the F number based on the voltage signal. If one time of achange amount of the F number is large, a level of the voltage signal ischanged by a hole effect. However, if the F number is to be graduallychanged to the optimum F number, the hole effect is restrained, thuspossible to exactly control the aperture amount.

[0022] In a case that the aperture blade is moved by the motor, it ispossible to appropriately drive the aperture blade irrespective of ahysteresis characteristic of the motor if the F number is to be changedonly to one of a first direction in which a numerical value decreases,and a second direction in which a numerical value increases.

[0023] Preferably, the image sensor outputs a still image signal when arecording instruction is applied, and the calculating means calculatesthe optimum F number in response to the exposure adjusting instruction,which is prior to the recording instruction.

[0024] The above described objects and other objects, features, aspectsand advantages of the present invention will become more apparent fromthe following detailed description of the present invention when takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 is a block diagram showing one embodiment of the presentinvention;

[0026]FIG. 2 is an illustrative view showing an aperture apparatus;

[0027]FIG. 3 is a circuit diagram showing a driver for driving theaperture apparatus;

[0028]FIG. 4 is a flowchart showing one portion of an operation of theFIG. 1 embodiment;

[0029]FIG. 5 is a flowchart showing another portion of the operation ofthe FIG. 1 embodiment;

[0030]FIG. 6 is a flowchart showing the other portion of the operationof the FIG. 1 embodiment;

[0031]FIG. 7 is a flowchart showing a further portion of the operationof the FIG. 1 embodiment;

[0032]FIG. 8 is a graph showing a relationship between a PWM value andan F number;

[0033]FIG. 9 is a graph showing a relationship between the PWM value anddriving voltage of the aperture apparatus;

[0034]FIG. 10 is a timing chart showing one portion of an operation ofan aperture blade in a prior art;

[0035]FIG. 11 is a timing chart showing one portion of an operation ofthe aperture blade in the FIG. 1 embodiment;

[0036]FIG. 12 is a timing chart showing one portion of an operation of aphotographing device and an aperture apparatus; and

[0037]FIG. 13 is a graph showing a relationship between the PWM valueand a required time that the aperture blade closes fully.

BEST MODE FOR PRACTICING THE INVENTION

[0038] Referring to FIG. 1, a digital camera 10 in this embodimentincludes a focus lens 12 and an aperture apparatus 14. An optical imageof an object is incident on a light-receiving surface of a photographingdevice 16 through the members. It is noted that either type of imagesensors, a CCD type or a CMOS type, may be adopted as the photographingdevice 16.

[0039] When a power switch 54 is operated, a system controller 50activates a power circuit 56, and the power circuit 56 supplies to awhole system DC voltage generated based on a battery 58. A CPU 46starts-up a signal processing block including a TG 18, a signalprocessing circuit 26, and others, and an encode block including a videoencoder 32, a monitor (display) 34, and others.

[0040] The timing generator (TG) 18 generates a timing pulse for drivingthe photographing device 16, and a raw image signal (camera signal)generated on the light-receiving surface is read out from thephotographing device 16 in response to the timing pulse. It is notedthat as for the timing pulse, in addition to a vertical transfer pulse,and a horizontal transfer pulse, there are an electric charge sweep-outpulse for sweeping electric charges generated by a charge-coupled device(not shown) to an overflow drain (not shown) during a non-exposure time,that is, non-electric charge accumulating period, and others.

[0041] The camera signal outputted from the photographing device 16 issubjected to a correlation double sampling and a gain adjustment in aCDS circuit 20 and an AGC circuit 22. The camera signal to which thegain adjustment is subjected is applied to the signal processing circuit26 via an A/D converter 24. The signal processing circuit 26 subjectsthe applied camera signal to signal processings such as a colorseparation, a white balance adjustment, a YUV conversion, and othersbefore outputting a YUV signal. The YUV signal is written into an SDRAM30 by a memory control circuit 28.

[0042] The YUV signal written in the SDRAM 30 is read out by a memorycontrol circuit 28 based on a read-out request outputted from a videoencoder 32. The read YUV signal is converted into a composite imagesignal by the video encoder 32, and a converted composite image signalis applied to a monitor 34. As a result, a moving image of an object(through image) is displayed on the monitor 34 in a real time fashion.

[0043] When an operator operates a shutter button 52, the systemcontroller 50 applies a corresponding state signal to the CPU 46. TheCPU 46 performs a focus adjustment and an exposure adjustment, andthereafter instructs a TG 18 and a JPEG CODEC 40 respectively to carryout an primary exposure and a compression process. The TG 18 subjectsthe photographing device 16 to the primary exposure, and reads out aresultant one screen of the camera signal from the photographing device16. The TG 18 is deactivated at a time of completing reading out onescreen of the camera signal. The read camera signal is converted intothe YUV signal according to the above-described procedure, and theconverted YUV signal is retained in the SDRAM 30. The JPEG CODEC 40reads out the YUV signal based on the primary exposure from the SDRAM 30through the memory control circuit 28, and subjects the read YUV signalto a JPEG compression. The resultant compressed YUV signal is recordedinto a memory card 48 by the CPU 46.

[0044] An aperture apparatus 14 is structured as shown in FIG. 2. Amotor 14 a is formed of two magnets 14 b, 14 c, and a moving coil 14 d.At the center of the moving coil 14 d, a shaft 14 e extending toward anoptical axis direction is provided, and a lever 14 f is attached to theshaft 14 e. Two aperture blades 14 g and 14 h are held at both ends in alongitudinal direction of the lever 14 f.

[0045] As a result of a current being supplied to the moving coil 14 d,the moving coil 14 d itself rotates, and the lever 14 d turns toward adirection perpendicular to the optical axis. The aperture blades 14 gand 14 h move toward an opposite direction to each other in a directionperpendicular to the optical axis. However, long holes 14 i and 14 jextending toward a moving direction are formed on the aperture blades 14g and 14 h, respectively, and pins 14 k and 14 m protruding toward theoptical axis direction are engaged with the long holes 14 i and 14 j,respectively. Consequently, a moving amount of the aperture blades 14 gand 14 h is restricted by the pins 14 k and 14 m.

[0046] When the pin 14 k contacts one end 141 i of the long hole 14 i,and the pin 14 m contacts one end 141 j of the long hole 14 j, anaperture OP defined by the aperture blades 14 g and 14 h opens mostwidely, and an F number shows a minimum value. In contrary, when the pin14 k contacts the other end 142 i of the long hole 14 i, and the pin 14m contacts the other end 142 j of the long hole 14 j, the aperture OPfully closes, which cuts-off an incident light toward the photographingdevice 16. The pin 14 m is connected to the aperture blade 14 h by anelastic member 14 n that likens to a spring, and elasticity toward whichthe aperture OP is closed is always applied to the aperture blade 14 h.In the vicinity of the moving coil 14 d, a hole element 14 p isprovided. The hole element 14 p produces a plus output and a minusoutput, and a plus output level changes according to a rotating degreeof the lever 14 f, i.e. the F number.

[0047] A driver 42 is structured as shown in FIG. 3. As a result of aPWM signal being applied from the CPU 46 to a terminal S1, the PWMsignal is applied to a non-inversion input terminal of an operationalamplifier 42 b via a smoothing circuit 42 a. At an output terminal ofthe operational amplifier 42 b, a level that corresponds to a duty ofthe PWM signal appears. This level is defined as a PWM output. The plusoutput and the minus output of the hole element 14 p shown in FIG. 2 areapplied to an inversion input terminal and the non-inversion inputterminal of an operational amplifier 42 c via terminals S2 and S3. At anoutput terminal of the operational amplifier 42 c, a level thatcorresponds to a difference of the plus output and the minus outputappears. This level is defined as a hole element output. The PWM outputand the hole element output are subjected to a differentialamplification process by an operational amplifier 42 d, and drivingvoltage Viris of the moving coil 14 d is obtained as a result thereof.Therefore, the driving voltage Viris is defined by a duty ratio of thePWM signal and the plus output level of the hole element 14 p, that is,the F number.

[0048] When the voltage is input, the CPU 46 processes flowcharts shownin FIG. 4 FIG. 7. First, a signal processing block and an encode blockare activated in steps of S1 and S3, respectively. In a step S5, a PWMsignal having the PWM value (=pulse width) of an initial value isapplied to the driver 42 so as to set the F number of the apertureapparatus 14 to the initial value. The initial value of the F number isa value that a predetermined value a is added to a minimum value Fmin.This prevents the pins 14 h and 14 m shown in FIG. 2 from colliding withthe one end 141 i of the long hole 14 i and the other end 141 j of thelong hole 14 j.

[0049] It is determined whether or not a vertical synchronization signalis produced in a step S7. The vertical synchronization signal isproduced at a head of each field, and if YES in the step S7, apre-exposure is instructed to the TG 18 in a step S9 and an exposurecorrection is performed in a step S11. It is determined whether or notthe shutter button 52 is half-depressed in a step S13, and the processesof steps S 7-S11 are repeated until YES is determined.

[0050] The TG 18 subjects the photographing device 16 to thepre-exposure in response to the pre-exposure instruction in the step S9,and reads out from the photographing device 16 the camera signalgenerated by the pre-exposure. As a result, a through image is displayedon the monitor 34 while the shutter button 52 is not depressed.

[0051] A luminance evaluation circuit 36 shown in FIG. 1 integrates a Ysignal generated based on the pre-exposure of a preceding field for aone frame period so as to evaluate a luminance evaluation value. In thestep S11, the F number is adjusted in such a manner as to obtain anoptimum exposure amount based on the luminance evaluation valueoutputted from the luminance evaluation circuit 36. At this time,basically, an exposure time period is a fixed value. However, when theoptimum exposure amount is not obtained unless the F number is set tothe minimum value Fmin, the F number is set to a value other than theminimum value Fmin by changing the exposure time period. Thus, it isprohibited to set the minimum value Fmin while the through image isdisplayed.

[0052] It is noted that the pre-exposure time period in the step S9 iscontrolled only by an electronic shutter function of the TG 18. That is,an output of an electric charge sweep-out pulse is intercepted at anexposure starting timing, and an output of the electric charge sweep-outpulse is resumed after reading out the electric charges accumulated inthe charge-coupled device.

[0053] If the shutter button 52 is half-depressed, a focus control isperformed in a step S15. More specifically, the focus lens 12 isgradually moved to the optical axis direction by controlling the driver44, the pre-exposure is instructed to the TG 18 in each step, and thefocus evaluation value based on the pre-exposure is fetched from thefocus evaluation circuit 38. Then, a focal point is detected based on aplurality of the fetched focus evaluation values so as to set the focuslens 12 to the focal point.

[0054] In a step S17, the luminance evaluation value is fetched from theluminance evaluation circuit 36 so as to calculate an optimum F numberthat defines the optimum exposure amount (=optimum value Fs), and anoptimum exposure time period based on the luminance evaluation value. Ina step S19, it is determined whether or not the calculated optimum valueFs satisfies a condition that Fmin smaller than (<) FS smaller than (<)Fth. Fth is a value larger by a predetermined value than the minimumvalue Fmin. When the optimum value Fs does not satisfy the condition,the process directly advances to a step S25. In contrary, when theoptimum value Fs satisfies the condition, the exposure time period ischanged according to Equation (1) in a step S21, and the optimum valueFs is changed to the minimum value Fmin, i.e. the minimum F number in astep S23 before advancing to the step S25. It is noted that in the stepS23, only the minimum value Fmin is determined as the optimum value Fs,and the aperture apparatus 14 is controlled in steps that follow S25.

[0055] Changed exposure time period=optimum exposure timeperiod*(Fmin/Fs)²  (1)

[0056] The PWM value (=PWMs) capable of setting the F number to theoptimum value Fs is calculated in the step S25, and changing widths b0and b1 of the PWM value are determined in a step S27. The changingwidths b0 and b1 are determined according to Equation (2).

b0=(initial value−PWMs)*(2/3)

b1=(initial value−PWMs)*(1/3)  (2)

[0057] The PWM signal having the PWM value of “initial value+b0” isapplied to the driver 42 in a step S29, and waits for a predeterminedtime period t0 in a step S31. In a step S33, the PWM signal having thePWM value of “initial value+b1” is applied to the driver 42, and waitsfor a predetermined time period t1 in a step S35. In a step S37, the PWMsignal having the PWM value of the PWMs is applied to the driver 42, andwaits for a predetermined time period t2 in a step S39. This graduallychanges the F number from the initial value to the optimum value Fs.

[0058] Upon completion of setting the F number, it is determined whetheror not the shutter button 52 is fully depressed in a step S41. If YES,the process advances from a step S43 to a step S45 in response to ageneration of the vertical synchronization signal so as to instruct theprimary exposure to the TG 18. Furthermore, the aperture apparatus 14 isactivated as a mechanical shutter at a predetermined timing in a stepS47.

[0059] A starting timing and an ending timing of the primary exposureare determined based on the optimum exposure time period calculated inthe step S17 or the exposure time period changed in the step S21. Inaddition, the start of the primary exposure is controlled by anelectronic shutter function of the TG 18, and the end of the primaryexposure is controlled by a mechanical shutter function of the apertureapparatus 14. That is, referring to FIG. 12, the TG 18 repeats toperform the electric charge sweep-out from a head of a one field periodduring which the primary exposure is carried out, and suspends theelectric charge sweep-out in a primary exposure starting timing. Thisstarts accumulating electric charges, i.e. the primary exposure. Theaperture apparatus 14 starts driving the aperture blades 14 g and 14 hin a primary exposure ending timing. The primary exposure is ended at atime that the aperture blades 14 g and 14 h are completely closed.

[0060] Upon completion of the primary exposure, the TG 18 reads out fromthe photographing device 16 the electric charges accumulated in thecharge-coupled device, that is, the camera signal. The read camerasignal is applied to the signal processing circuit 26 via a CDS circuit20, an AGC circuit 22, and the A/D converter 24 before being convertedinto the YUV signal. The converted YUV signal is stored into the SDRAM30 by the memory control circuit 28.

[0061] The YUV signal stored in the SDRAM 30 is subjected to a recordingprocess in a step S49. More specifically, the JPEG CODEC 40 isinstructed to carry out a compression process, and a compressed YUVsignal generated by the JPEG CODEC 40 is recorded into the memory card48. The process returns to the step S5 after completing the recordingprocess.

[0062] A relationship between the PWM value and the F number is shown inFIG. 8. The F number decreases in proportion to an increase of the PWMvalue. However, if the PWM reaches a predetermined value, the pin 14 kshown in FIG. 2 contacts the one end 141 i of the long hole 14 i, andthe pin 14 m contacts the other end 141 j of the long hole 14 j. At thistime, the F number becomes the minimum value Fmin, and the F numberkeeps retaining the minimum value Fmin even if the PWM value exceeds thepredetermined value.

[0063] A relationship between the PWM output and the driving voltageViris is shown in FIG. 9. The driving voltage Viris increases inproportion to an increase of the PWM value, which decreases the Fnumber. However, an output of the hole element 14 p remains constantregardless of the increase of the PWM value after the aperture OP shownin FIG. 2 is opened most widely. This rapidly increases the drivingvoltage Viris, greatly consuming electricity. That is, a consumedelectricity when setting the F number to the minimum value Fmin spendsmore electricity than setting the F number to a value other than theminimum value Fmin. In this embodiment, it is prohibited to set the Fnumber to the minimum value Fmin when outputting the through image,which prevents the consumed electricity from increasing. This makes itpossible to prolong longevity of the battery 58.

[0064] Furthermore, if the PWM value is rapidly changed, the apertureblades 14 g and 14 h are greatly moved. At this time, a transientresponse as shown in FIG. 10 occurs to an output waveform of the holeelement 14 p. In this embodiment, the PWM value is to be graduallyupdated when setting the F number to the optimum value Fs so that theoutput waveform of the hole element 14 p changes as shown in FIG. 1.This restraints an unstable movement due to the transient response, thuspossible to exactly set the F number. Furthermore, there is a hysteresisin the moving coil 14 d that drives the aperture blades 14 g and 14 h,and in this embodiment, the aperture blades 14 g and 14 h only move to asingle direction when setting the F number to the optimum value Fs. Thismakes it possible to appropriately adjust the F number regardless of thehysteresis.

[0065] A relationship between the PWM value and a required time periodwhen activating the aperture apparatus 14 as the mechanical shutter (arequired time period for the aperture OP to be fully close) is shown inFIG. 13. The aperture OP is opened widely in proportion to an increaseof the PWM value, and therefore, the required time period for fullyclosing the aperture OP becomes longer approximately in proportion tothe increase of the PWM value. It is noted that in the vicinity of an Xof the minimum value Fmin, the required time period drastically becomeslong. That is, a big difference in the required time occurs between theminimum value Fmin and the predetermined value Fth. This, in thevicinity of the X of the minimum value, results in a very largedifference in the required time period when a difference occurs betweenthe desired F number and the F number actually set.

[0066] In a case of, in reality, setting the minimum value Fmin in spiteof being intended to set a value slightly higher than the minimum valueFmin, for example, a large difference occurs to the required timeperiod. In this embodiment, when the calculated optimum value Fs of theF number belongs to a range of Fmin (<) smaller than Fs (<) smaller thanFth, the optimum value Fs is changed to the minimum value Fmin. Thismakes it possible to exactly control the mechanical shutter.

[0067] It is noted that when outputting the through image, it isprohibited to set the F number to the minimum value Fmin in order torestraint the consumed electricity from increasing. In contrary, the Fnumber being changed to the minimum value Fmin when the optimum F number(=Fs) at a time of the primary exposure is included in theabove-described range attributes to a fact that a time period that the Fnumber is set to the minimum value Fmin for the primary exposure isquite short, an increase of the consumed electricity is not a majorproblem, and it is more important to obtain as much exposure amount aspossible than restraining the consumed electricity.

[0068] Although the present invention has been described and illustratedin detail, it is clearly understood that the same is by way ofillustration and example only and is not to be taken by way oflimitation, the spirit and scope of the present invention being limitedonly by the terms of the appended claims.

1. (Amended) A video camera that displays a moving image of an objectphotographed by an image sensor in a real time fashion, and records intoa recording medium a still image of said object photographed by saidimage sensor in a desired timing, comprising: an aperture blade foradjusting an amount of an incident light into said image sensor bymoving toward a direction perpendicular to a light axis; a restrictingmember for restricting a moving amount of said aperture blade in orderto define a minimum F number; a prohibiting means for prohibiting asetting of said minimum F number when displaying said moving image; andan allowing means for allowing a setting of said minimum F number whenrecording said moving image.
 2. A video camera according to claim 1,wherein said aperture blade has a hole extending to a moving direction,and said restricting member has a protruding portion engaged with saidhole.
 3. A video camera according to claim 1, further comprising a motorfor transmitting power to said aperture blade.
 4. (Amended) A videocamera: comprising an aperture blade for adjusting an amount of anincident light into an image sensor by moving toward a directionperpendicular to a light axis; a restricting member for restricting amoving amount of said aperture blade in order to define an openingterminal corresponding to a minimum F number; an optimum F numbercalculating means for calculating an optimum F number that defines anoptimum exposure amount when an exposure adjusting instruction isapplied; an exposure time period specifying means for specifying anexposure time period that defines in cooperation with said optimumexposure amount said minimum F number when said optimum F number isincluded in a predetermined range; an aperture blade moving means formoving said aperture blade to said opening terminal when said optimum Fnumber is included in said predetermined range; a cutting-off means forcutting-off an incident light into said image sensor by completelyclosing said aperture blade in a timing according to said exposure timeperiod when a recording instruction is applied after said exposure timeperiod adjusting instruction; and a recording means for recoding a stillimage signal outputted from said image sensor after a cutting-off bysaid cutting-off means.
 5. (Amended) A video camera according to claim4, wherein said cutting-off means includes a transmitting means fortransmitting power to said aperture blade, and said predetermined rangeis present in the vicinity of said minimum F number.
 6. A video cameraaccording to claim 5, wherein said aperture blade has a hole extendingtoward a moving direction, and said restricting member has a protrudingportion engaged with said hole.
 7. (Deleted)
 8. (Deleted)
 9. (Amended) Avideo camera, comprising: an image sensor for generating an image signalcorresponding to an optical image irradiated onto a light-receivingsurface; an aperture blade for adjusting an incident light amount intosaid image sensor by moving toward a direction perpendicular to a lightaxis; a calculating means for calculating an optimum F number of saidaperture blade based on said image signal; and a changing means forchanging the F number of said aperture blade to said optimum F number,wherein said changing means gradually changes said F number to only oneof a first direction in which a numerical value decreases, and a seconddirection in which the numerical value increases.
 10. A video cameraaccording to claim 9, further comprising a hole element that generates avoltage signal corresponding to the F number of said aperture blade,wherein said changing means changes said F number based on the voltagesignal.
 11. (Deleted)
 12. A video camera according to claim 9, whereinsaid image sensor outputs a still image signal when a recordinginstruction is applied, and said calculating means calculates saidoptimum F number in response to an exposure adjusting instruction, whichis prior to said recording instruction.